Friday, May 8, 2009

Cell Membrane 3


The picture at left is a membrane transport protein known as a sodium-potassium pump. Details are found at the OPM site of University of Michgian. The horizontal red and blue lines represent the cell membrane outline.

This protein, or actually set of inter-working proteins, has about 2500 amino acids. It is necessary for the cell to be able to pump out positively charged sodium particles so that the cell doesn't become too attractive to water, which can move in by osmosis and explode the cell. There are many negatively charged proteins and positive particles inside the cell, and this pump keeps the positive ion level down. The action of the pump is part of what is called active transport, when particles are moved against a gradient and/or are unable to diffuse through the membrane. More information can be found at the Wikipedia site for Sodium-pump.

There are other reasons for a sodium gradient, such as stimulation of nerve cells. These cells must move ions quickly in order for them to pass a charge along their membranes from one end to the next and from one cell to another. Different cells have specialized needs and the membrane proteins must be able to handle them. Muscle cells need calcium in order to contract. Cells must move food in and waste products out, and must respond to changes in levels of hormones in the blood stream. All these take individually specialized membrane proteins, since the rest of the membrane will not allow large proteins and food in or out.

There have been discoveries of proteins which are completely different and yet have some of the same properties. They are composed of different sets of amino acids (the building blocks of proteins), yet they fold in similar ways, which allows them to do similar work. However, folding itself is rarely found in randomly arranged amino acid sequences, as reported by protein laboratories in papers such as this by Moffet and Hecht (the introduction is quite interesting). Therefore, though the numbers of proteins which can carry on a specific job may increase, the total is still vanishingly small. The calculations of just how many are being worked upon now by many on both the materialistic and design advocate "sides." Considering the low probabilities (such as 1 in 10^65 viable for a protein of 100 amino acids calculated by Hubert Yockey), the numbers would have to be amazingly large to make a dent. That seems unlikely since many proteins are believed to be very close to the same as they were at the very start of life. (On a different note but related: many proteins are being found unique for particular species.)

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